Before Daniel Ellsberg leaked the Pentagon Papers in 1971, he paid a fateful visit to a New Mexico prison, not far from the Arizona border.

The now-notorious American whistleblower went to see Randy Kehler, the imprisoned draft dodger whose speech at an anti-war rally in August, 1969, sparked an epiphany in Ellsberg. The loyal Pentagon strategist wanted Kehler to know what he had inspired - so, in the prison's visiting room, sitting across from Kehler, he revealed his plan: To leak all 7,000 pages of a top secret government study on the Vietnam War to the press, proving successive U.S. presidents had lied to the American people, and hoping to stop the "unjustified killing" of scores more Vietnamese.

"When I left I thought, Jesus Christ, that visitors centre could be bugged. I've just told the federal government what I'm going to do," says Ellsberg, 78, over breakfast at a Toronto hotel. He was in town for the world premiere of
The Most Dangerous Man in America: Daniel Ellsberg and the Pentagon Papers, a documentary by California filmmakers Judith Ehrlich and Rick Goldsmith, at the Toronto International Film Festival.

Lucky for him, no one at the New Mexico Corrections Department was listening. And in fact, a sign he spotted in the vice-warden's office, titled "Federal Code of Ethics" provided assurance that he was doing the right thing.

"The first thing on it was that every federal employee, 'shall put loyalty to the highest moral principals and to country above loyalty to government persons, part or department.' My first thought was, that's what I'm doing," he says. "But that was an absolute contradiction of the bureaucrat's operating code: agency first, then person. [An authority]higher than the president? Unthinkable."

The documentary, in which Ellsberg features prominently, has since been nominated for an Academy Award and includes interviews with several key players, including a surprisingly contrite Egil Krogh. Krogh is the presidential aide who helped forge the "White House Plumbers" - a covert investigations team that later became famous for the Watergate break-ins - to dig up dirt on Ellsberg. Ehrlich is the first to say the documentary paints Ellsberg as heroic for helping turn public opinion against the war - but it also makes it clear that many saw him as a traitor.

Once a top military strategist entrusted with high-level security clearance, Ellsberg is Oppenheimer-esque, a man who put his tremendous intellect to work that ultimately proved destructive. When he was still a loyal Pentagon analyst in the mid-1960s, he knew what the public didn't: Though the Johnson administration was saying otherwise, an escalation of the Vietnam War was in the works. Secretary of Defense Robert McNamara ordered Ellsberg to find evidence to help sell the expansion and, Ellsberg remembers, "an order from McNamara was like an order from God." He became the war's unseen planner.

In 2004, with the U.S. embroiled in two sprawling wars, Ehrlich and Goldsmith arrived at the same conclusion: "[Ellsberg's]story was just so obviously relevant now," Goldsmith says.

On his flight to Toronto, Ellsberg began compiling a list of parallels between the Vietnam and Afghanistan wars. He even woke in his hotel room at 4 a.m. to add to it. At breakfast the next morning, he pulls a yellow pad of ruled paper from his briefcase, flipping through page after page of small, neat script.

"I got to number 97," he says matter-of-factly. "Number one," he says derisively, "we can't back down now, the stakes are too high. The investment has been made."

Ellsberg now encourages others in government to bring greater transparency to the way wars are conducted, and over breakfast offered a disheartening take on present-day escalations. Less than two weeks before our interview, U.S. General Stanley McChrystal, commander of the U.S. forces in Afghanistan, had handed President Barack Obama three scenarios for a surge, ranging from 10,000 to 45,000 new troops. (Obama ultimately settled on 30,000.)

"I'll say this as certain as I can be: There isn't a chance in the world McChrystal is telling him that 45,000 [troops]will achieve any kind of significant success. All that will do is prolong the stalemate," Ellsberg said. "I'm certain Obama is hearing figures of hundreds of thousands to achieve any significant or lasting success there."

"When President Johnson said in 1965, 'I'm sending 50,000 men,' he knew that all of his militaries had recommended 500,000 to one million," Ellsberg added. "What we need [now]is for somebody [on the]inside to take his career in hand, kiss it off and say, 'No, the truth is, Congress, here's the estimates the President is really seeing.'"

The Most Dangerous Man in America: Daniel Ellsberg and the Pentagon Papers opens Friday in Toronto and airs next month on PBS.